/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.catalina.tribes.util;

import java.util.Collection;
import java.util.concurrent.*;

public class ExecutorFactory {

	public static ExecutorService newThreadPool(int minThreads, int maxThreads, long maxIdleTime, TimeUnit unit) {
		TaskQueue taskqueue = new TaskQueue();
		ThreadPoolExecutor service = new TribesThreadPoolExecutor(minThreads, maxThreads, maxIdleTime, unit, taskqueue);
		taskqueue.setParent(service);
		return service;
	}

	public static ExecutorService newThreadPool(int minThreads, int maxThreads, long maxIdleTime, TimeUnit unit, ThreadFactory threadFactory) {
		TaskQueue taskqueue = new TaskQueue();
		ThreadPoolExecutor service = new TribesThreadPoolExecutor(minThreads, maxThreads, maxIdleTime, unit, taskqueue, threadFactory);
		taskqueue.setParent(service);
		return service;
	}

	// ---------------------------------------------- TribesThreadPoolExecutor Inner Class
	private static class TribesThreadPoolExecutor extends ThreadPoolExecutor {
		public TribesThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, RejectedExecutionHandler handler) {
			super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, handler);
		}

		public TribesThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory,
		                                RejectedExecutionHandler handler) {
			super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory, handler);
		}

		public TribesThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory) {
			super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory);
		}

		public TribesThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
			super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
		}

		@Override
		public void execute(Runnable command) {
			try {
				super.execute(command);
			} catch (RejectedExecutionException rx) {
				if (super.getQueue() instanceof TaskQueue) {
					TaskQueue queue = (TaskQueue) super.getQueue();
					if (!queue.force(command)) {
						throw new RejectedExecutionException("Queue capacity is full.");
					}
				}
			}
		}
	}

	// ---------------------------------------------- TaskQueue Inner Class
	private static class TaskQueue extends LinkedBlockingQueue<Runnable> {
		private static final long serialVersionUID = 1L;

		ThreadPoolExecutor parent = null;

		public TaskQueue() {
			super();
		}

		public TaskQueue(int initialCapacity) {
			super(initialCapacity);
		}

		public TaskQueue(Collection<? extends Runnable> c) {
			super(c);
		}

		public void setParent(ThreadPoolExecutor tp) {
			parent = tp;
		}

		public boolean force(Runnable o) {
			if (parent.isShutdown())
				throw new RejectedExecutionException("Executor not running, can't force a command into the queue");
			return super.offer(o); //forces the item onto the queue, to be used if the task is rejected
		}

		@Override
		public boolean offer(Runnable o) {
			//we can't do any checks
			if (parent == null) return super.offer(o);
			//we are maxed out on threads, simply queue the object
			if (parent.getPoolSize() == parent.getMaximumPoolSize()) return super.offer(o);
			//we have idle threads, just add it to the queue
			//this is an approximation, so it could use some tuning
			if (parent.getActiveCount() < (parent.getPoolSize())) return super.offer(o);
			//if we have less threads than maximum force creation of a new thread
			if (parent.getPoolSize() < parent.getMaximumPoolSize()) return false;
			//if we reached here, we need to add it to the queue
			return super.offer(o);
		}
	}
}
